Wellspring has signed a 15-year lease for the entire 44th floor, spanning 14,698 square feet, at the 1.1-million-square-foot office tower between East 39th and East 40th Streets, The Real Deal first reported.

The private equity firm will relocate from its current location at 390 Park Avenue, also known as the Lever House, between East 53rd and East 54th Streets.

Asking rents at 605 Third Avenue were in the mid-$80s per square foot, according to a source with knowledge of the transaction.

Fisher Brothers built 605 Third Avenue in 1963 and finished a $25 million capital improvement program there in early 2016, as per a news release. The building is currently 96 percent leased with tenants including television station Univision, engineering firm Aecom and fintech companyBroadridge Financial Solutions, which took four floors at the building in November 2018, as Commercial Observer previously reported.